1. Field of the Invention
The present invention relates to light-control devices and to methods of fabricating such devices (the term "light" being used herein to refer in the generic sense to visible light and infrared, ultraviolet and microwave radiation in neighboring portions of the electromagnetic spectrum). More particularly the present invention relates to light-control devices in which small light-control elements are selectively oriented by an electric or magnetic field, and to methods of manufacturing such devices.
2. Description of the Prior Art
Various field-addressable devices have been proposed for selectively controlling incident light (e.g., regulating its transmission, reflection, diffraction or absorption). The present invention pertains to active devices of this type (i.e., capable of rapid and recurring changes in light-control effect) as opposed to inactive devices (i.e., primarily intended for a relatively permanent light-control effect). Such active light-control devices have various applications, e.g., light modulators, display screens, image converters or image intensifiers.
U.S. Pat. No. 2,290,581 discloses an early electro-optic converter in which graphite or aluminum particles, suspended in a liquid medium, are selectively aligned by a scanning electron-gun to modulate the passage of light and provide a viewable image. Similar light-control devices, using dipole particles in liquid suspension and electric orienting fields, are disclosed in U.S. Pat. Nos. 3,257,903; 3,512,876 and 3,527,525.
Such prior art approaches present certain difficulties or disadvantages, for example, high fabrication cost, fragile packaging and high sensitivity to environmental change. Also, these devices have a slow recovery time, caused by their reliance on Brownian movement for returning dipole particles to an unoriented condition.
Recently a new light-control approach substantially avoiding the above-mentioned problems and disadvantages was disclosed by L. F. Frank and J. Y. Kaukeinen in Research Disclosure No. 15535, Vol. 155, pp. 64-71, March, 1977, published by Industrial Opportunities Ltd., Homewell, Havant, Hampshire, PO9 IEF, United Kingdom. This new concept provides a light-control device in which a plurality of light-control elements are dispersed in an elastomeric matrix. As in the prior liquid systems, the light-control elements of this new device have a configuration which can provide both a relatively small and a relatively large obstruction to the passage of light, i.e., having large and small silhouettes, and the dipole characteristic of aligning in a common orientation in an electric or magnetic field. However, in the new approach the elastomeric matrix restrains the elements from random movement within the layer and has an elasticity which allows orientation of the elements under the influence of the field. Upon termination of the field, the elements are quickly returned to their retained orientation by restoring forces of the elastic matrix. The elements disclosed in the aforementioned publication can be employed for area-wise light control, e.g., as camera shutters, or can be used in cooperation with various imagewise field producing means, e.g., a photoconductor, a discharge stylus, or a patterned electrode, to provide new and useful image display panels.
This new approach, utilizing dipole particles in a solid elastomeric material, affords many operational and fabrication advantages; however, in some instances, difficulties have been encountered because of irregularities in the size, shape and/or distribution of the light-control elements.